1. Field of the Invention
The present invention relates to a valve operating system for a multi-cylinder internal combustion engine, and particularly, to a valve operating system in a multi-cylinder internal combustion engine having an intake and exhaust valve operating (hereinafter also referred to as "operating/stopping") switch-over means capable of switching over the operation and non-operation or stoppage of an intake and exhaust valve for at least one of a plurality of cylinders, with each of the valve operating/stopping switch-over means including means for causing operation in response to a hydraulic pressure.
2. Description of the Prior Art
A valve operating system in which in at least one of a plurality of cylinders, an intake valve is closed and stopped for bringing the cylinder into its non-operating or stopped state is conventionally known, for example, from Japanese Utility Model Publication No. 24888/90 and Japanese Patent Publication No. 50284/90.
It is necessary not only to close and stop the intake valve, but also to close and stop the exhaust valve when the cylinder is inoperative or stopped. For this purpose, a valve operation and stoppage switch-over means may be provided for each of the intake and exhaust valves of a cylinder. However, to avoid combustion gas remaining within the stopped cylinder, when the cylinder is stopped, it is necessary to stop the intake valve prior to stoppage of the exhaust valve. On the other hand, if air is supplied into and retained in the cylinder in a condition in which the supplying of fuel has been cut, it is possible to prevent the escape of oil. In this case, it is necessary to stop the intake valve prior to stoppage of the exhaust valve. When the valve operation and stoppage switch-over means is of a hydraulically operated type, in order to provide a time difference between the stoppage of the intake valve and the stoppage of the exhaust valve, when the cylinder is stopped, hydraulic pressure control valves may be connected independently to the valve operation and stoppage switch-over means for the intake and exhaust valves, respectively, so that the operation of the hydraulic pressure control valves are controlled with a time difference. However, then two hydraulic pressure control valves are required, resulting not only in an increase in number of parts, but also in an increased space for disposition of the hydraulic pressure control valves.